Sunday Times Teaser 2525
by DJT Hogg
Published: 13 February 2011 (link)
“Sandwich numbers” are those of the form BFB, where B is the bread and is a single digit, and F is the filling of any length: BFB has to be divisible by F. For example, 11371 is a sandwich with filling 137 since 11371 = 83 x 137. Incidentally, all of 21372, 31373, … , 91379 are also sandwich numbers, and these nine are said to make up a “sandwich box”.
The filling in my sandwich box today is the smallest beginning with a 3.
What is my filling?